Once bitten

Mornings are busy at the Ezell house, and that particular morning in March---uncharacteristically soggy for a Texas spring---was no exception. With her husband already on his way to work, small-animal veterinarian Kristen Ezell strapped her 3-month-old son and 2-year-old daughter into their car seats, planning to drop them off at daycare on her way to her clinic, where she had a full day of patients scheduled.

The driveway circled the house, past the fence where Fancy, Ezell’s 11-year-old Quarter Horse mare, stood in her pasture. Even from the moving car, Ezell could tell something was wrong: “She was facing me, and I immediately noticed she looked odd. I thought maybe she was colicking from the way she was covered in mud and standing awkwardly, but I couldn’t tell for sure. So I just kept going around the driveway and back to the house. I changed into my boots and headed out through the mud to Fancy.”

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Ezell dropped the idea of colic as she approached Fancy and got a better look at her mare: “Her entire head was swollen. Particularly her left eye---that was shut entirely. My first thought was that she’d been bitten or stung by something.”

Looking closer, Ezell discovered two small, identical wounds, both bleeding, just above Fancy’s left eye. “I knew then that this was most likely a snakebite and that my plans for the morning had changed dramatically,” she says.

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Fancy’s head was too swollen for a halter to fit, so Ezell looped the one she was carrying around the mare’s neck and walked her toward the barn. She’d seen a snakebitten horse in veterinary school, and she knew that the bigger danger to Fancy came not from the toxic venom but from the swelling.

“Snakebites in small animals are usually bad news because of the dose of venom relative to the size of the animal,” she explains. “But horses are so big that’s not really the danger; instead, it’s the swelling associated with the bite that is the concern. Horses are typically bitten on their heads as they graze, and the resulting swelling can completely close off their airways, causing them to suffocate. The one we saw in veterinary school ended up needing a tracheotomy in order to breathe.”

Corticosteroids could combat the swelling, but Ezell knew her mare would require much more care and monitoring than she was able to provide. “I couldn’t just throw medications at her then leave her all day,” says Ezell. “So I called [local veterinarian] Dr. Judd.”

Robert Judd, DVM, of Judd Veterinary Clinic in Hewitt, Texas, told Ezell it was OK to give Fancy Banamine to make her comfortable while bringing her to his clinic immediately. “I hooked up the trailer,” she says, “loaded the kids into the truck, loaded Fancy into the trailer and headed back down the driveway.”

Damage control

Fancy’s condition was a familiar sight to Judd. “We actually see four or five snakebites a year,” he says. “If I see a horse with a grossly swollen head, it’s one of the first things I’ll think of, especially in the spring when it’s warming up and the snakes are beginning to be active again.”

Judd examined the spot above Fancy’s eye where Ezell had found the two wounds and agreed that the mare had been bitten. And, given the time of year and the environment the mare lived in, the culprit was most likely a rattlesnake.

“We have 20 acres of land with a lot of rocky outcrops where snakes like to be,” says Ezell. “In this area, you can get entire dens of them.” The family had had a close encounter once before---when Ezell’s husband stepped out on the back porch and found a large rattler stretched along the length of the doorway---and it wasn’t difficult to imagine how Fancy may have nuzzled one in curiosity or even rolled onto one as she enjoyed the early spring mud.

Next Judd started an intravenous line and began delivering medications, along with DMSO, to combat the pain and swelling as well as penicillin and a tetanus booster vaccine. He also began administering fluids in a slow drip. Fancy would be unable to drink on her own until the swelling in her head diminished, and dehydration can be a fatal complication.

To combat the effects of the snake venom, Judd administered a liter of snake antivenin, produced from the hyperimmune plasma of other horses. Rattlesnake venom is hemotoxic, meaning it destroys red blood cells as well as other body tissues. It also disrupts blood clotting and, if the dose of toxin is large enough, can do enough damage to cause organ failure. Hyperimmune plasma is drawn from the blood of horses who have high levels of antibodies to the snake venom. When administered to a recently bitten horse, the antibodies in the hyperimmune plasma bind with and neutralize any toxins that are still circulating in the bloodstream. However, this treatment cannot “undo” any damage the toxins have already done. For that reason, antivenin is most effective when given soon after the bite occurs.

Ezell could not know exactly when Fancy had been bitten, but she and Judd opted to use the antivenin anyway, in case it might still be able to do some good.

Fancy’s head remained grotesquely swollen, but the mare was beginning to look a bit more comfortable. All anyone could do for her now was to watch and wait to see how well she would recover as the venom would continue to affect her system. The mare would need to be monitored round-the-clock for several days to watch for potential cardiac or neurological complications or other signs of damage to internal organs. The site of the bite would also need to be watched for signs of infection or necrosis (tissue death).

“A horse in this condition really needs to be watched 24-7 for several days,” says Judd. “If that’s your only job you can do it, but neither of us was in that position.”

Ezell and Judd decided to refer Fancy to a larger veterinary clinic, Brazos Valley Equine Hospital (BVEH) in Salado, Texas, which had the staff to provide the constant attention the mare needed. Once Fancy was on her way, Ezell got the rest of her morning back on track.

Supportive care

“The mare was stable when she arrived,” says John C. Janicek, DVM, who took over Fancy’s case at BVEH, “and doing pretty well, considering she’d been bitten in the head by a snake.”

Air was passing through Fancy’s right nostril, but swelling had blocked the left. Janicek disassembled a large syringe and inserted the barrel into her still-open nostril. With that tube in place, Fancy would still be able to breathe even if the swelling progressed.

Fancy was well hydrated with strong vital signs. The distance of the bite from any major organs was helpful, says Janicek. “So often the small animals are bitten on the torso or legs and they will go into respiratory and heart failure right away. The sheer size of horses not only dilutes the venom, but keeps it from reaching the major organs as easily.” As for Fancy’s mental outlook, he adds, “I wouldn’t say she was happy, but she was bright and alert.”

The state of Fancy’s left eye, hidden underneath the tightly swollen lid, was a significant concern. “We were worried about what damage there might have been to the cornea,” says Janicek, “but at that point it was still too swollen to examine. However, you could tell that the globe/anterior chamber were still normally inflated.”

Fancy remained under observation at BVEH for four days, with continued supportive medications and intravenous fluids. Gradually, the swelling receded until she could once again breathe through both of her nostrils as well as eat and drink.

“Dr. Judd told me that normally horses need to be on fluid for four or five days after a bite,” says Ezell. “But she bounced back in three. This may have been because of the antivenin we gave her. I think people need to consider that when deciding if it’s worth giving antivenin. It’s an extra expense, but what you save in days of fluid therapy could make it worthwhile.”

Once the swelling was down, Fancy’s eye could be examined. “We saw a small abscess on her cornea,” says Janicek. “It could have been from a nick of a fang or it could have been from her rubbing her eye immediately after the bite.” Whatever the cause, the treatment was the same: antibiotic ointment and atropine to keep the pupil dilated until the cornea could heal.

Fancy’s head was still slightly swollen when she returned home the following Saturday, but she was feeling and acting almost normal.

“We didn’t see any external necrosis of the tissue around the bite area, which was a relief,” says Ezell. “She wasn’t able to close her eye fully to blink, which was keeping the eye from being naturally lubricated and irritating the ulcer. So we just kept using antibiotic drops until the swelling resolved and she was able to blink completely on her own again.”

Before long, Fancy was back out in the pasture with her herd, with no apparent lingering effects from her ordeal. “She returned immediately to her lead-mare position,” says Ezell. “She’s the head honcho out there.”

The American Association of Equine Practitioners includes a vaccine against the toxin of the Western diamondback rattlesnake on its list of risk-based vaccination guidelines---a fact Ezell wasn’t aware of until Judd told her. “I vaccinate all my dogs, but it had never crossed my mind for the horses,” she says. “I’m certainly thinking about the benefit of it now.”

What she’s not going to do is hunt for the snake that bit Fancy. “People have asked me if I’m going to go looking for it to get revenge,” Ezell says. “Why would I do that? I don’t want to get myself bit. We will definitely be alert and careful now, but I’m not going to go looking for it.”